DESCRIPTION (Applicant Abstract): Rationale - The overall goal is to integrate an organized program of improved care of depression into the management of other chronic diseases in primary care. Diabetes mellitus was selected for study because of its prevalence and its large impact on patients and society. If a Depression Care Program (DCP) improves disability and/or disease outcomes among diabetics, it would help establish the core importance of recognition and management of depression for chronic disease management in primary care. Research goals - (1) We will develop population-based data in a managed care setting concerning the effects of depression on the societal impacts of diabetes and on the quality of diabetes (self)-management. By (self)-management we refer to both patients' and providers' roles in ongoing care of a chronic illness. (2) We will evaluate a generalizable and economically feasible Depression Care Program (DCP) for population-based management of depression among patients with diabetes mellitus. These goals will be achieved by two related studies. Aims of Study 1: Study 1 will assess the impact and management of depressive illness among diabetic patients, in an epidemiologic study, which will include patients with and without depression. Study 1 will assess the effects of major depression on societal impacts of diabetes (health care costs and disability) and on the quality of diabetes (self) management. These analyses will control for medical co-morbidity and baseline severity of diabetes. Aims of Study 2: We will evaluate whether a Depression Care program (DCP) for major depression in adult patients with Type 2 diabetes mellitus improves depression outcomes, disability outcomes, and glycemic control (as measured by HemoglobinA1C). Secondary process and outcome measures will include adherence to antidepressant and to diabetic medications, severity of symptoms related to diabetes, self-efficacy in managing diabetes, adherence to diabetes (self) management regimens (diet, exercise, glucose monitoring and medications), and health care utilization and costs. We will assess the cost-effectiveness of the DCP relative to care as usual. Data collection: We will carry out these studies by assessing diabetes and depression status in 4500 diabetic patients. Among Type 2 diabetics with major depression, 290 eligible and willing patients will be randomly assigned to a Depression Care Program or to Usual Care, We will evaluate the effectiveness of the Depression Care Program using self-report data collected at baseline, 3, 6, 12 and 24 months, and by HbA1C values assessed at baseline, 6, 12 and 24 months.